The obtention of vanadium values from vanadium-containing materials is effected in a wide variety of processes. For example, the vanadium-containing material can be subjected to the action of sulfuric acid, sodium hypochlorite, hydrochloric acid, nitric acid, etc. In addition, the prior art has also utilized certain ammonium salts such as ammonium chloride, ammonium sulfate, etc., as the precipitating agent whereby insoluble vanadium salts are formed. However, each of the prior art methods possesses certain disadvantages. For example, when utilizing acidic compounds such as hydrochloric acid, nitric acid, sulfuric acid, etc., the problem of clean-up of unwanted chemical compounds necessitates the use of relatively expensive and complicated apparatus in order to avoid the problem of polluting the environment. Furthermore, when utilizing ammonium salts such as ammonium chloride, ammonium sulfate, etc., the problem of an eventual buildup of chlorine or sulfate ions is present. This buildup is unwanted in view of the fact that the mother liquor will, after the caustic leach, eventually contain an amount of salts such as sodium chloride or sodium sulfate which are of insufficient caustic strength to take the vanadium into solution during the leaching operation.
A particular source of vanadium bearing materials may be obtained from the conversion of black oil to desired products. Black oil which may comprise the bottoms from a crude column or a vacuum tower is converted to lighter products such as distillate hydrocarbons which may be used as gasoline, jet fuel, fuel oil, gas oil, etc., in the presence of a catalyst comprising a vanadium sulfide precursor. In this conversion process using a vanadium-containing compound as a catalyst, the recycle stream resulting from the process is reinserted in the process flow stream at the beginning of the process. This recycle stream supplies a major portion of the catalyst to the process. However, the vanadium-containing material will tend to build up during the operation of the process which includes the aforementioned recycle stream. Therefore, a drag stream which is rich in vanadium is removed from the aforesaid recycle stream. This drag stream which is rich in vanadium values may be utilized as one source of vanadium, said drag stream itself being subjected to an oxidation process whereby the vanadium is present as an oxide in its highest valence form. However, in addition to the vanadium which is present, the drag stream or vanadium-containing source will also contain other metal impurities such as nickel, iron, etc. Therefore, to effect a more efficient operation with respect to the conversion of black oil it is necessary to remove these impurities in order that the vanadium catalyst will possess the desired activity level. As hereinafter set forth in greater detail, it will be shown that desired vanadium values may be obtained utilizing the novel process of the present invention.
This invention relates to a process for the recovery of vanadium values from vanadium-containing sources or materials. More specifically, the invention is concerned with an improvement in a process for the recovery of vanadium values whereby said vanadium may be recovered in a more economical and simple manner.
In addition to the use of vanadium as a catalyst for the conversion of black oil to lighter products, vanadium values such as vanadium metal or vanadium oxide are also useful for many purposes in the chemical industry. For example, vanadium metal may be used as the target material for X-rays, in the manufacture of steel or in the manufacture of vanadium compounds such as catalysts or alloys. Likewise, vanadium oxides such as vanadium pentoxide, are used as the starting material for other vanadium salts, as a catalyst for the oxidation of sulfur dioxide, as a catalyst for organic reactions, as a ceramic coloring material, for inhibiting ultra-violet transmission in glass, in black inks, in photographic developers, in dyeing textiles, in medicine, etc.
It is therefore an object of this invention to provide a process for recovering vanadium values from vanadium-containing sources.
A further object of this invention is found in an improvement in the process for obtaining vanadium values from vanadium-containing sources whereby the process may be effected in a more advantageous economic manner.
In one aspect an embodiment of this invention resides in a process for the recovery of vanadium values from a vanadium bearing source which comprises leaching said vanadium bearing source in an ammoniacal medium at an elevated temperature and pressure, separating the soluble ammonium vanadates from insoluble metal impurities, precipitating said soluble ammonium vanadates, separating the solid ammonium vanadates from the mother liquor, and recovering the desired vanadium values.
A specific embodiment of this invention is found in a process for the recovery of vanadium values from a vanadium bearing source which comprises leaching said vanadium bearing source in an ammoniacal medium at a temperature in the range of from about 50.degree. to about 300.degree. C. and a pressure in the range of from about 1 to about 200 atmospheres, separating the soluble ammonium vanadates from insoluble metal impurities, cooling said soluble ammonium vanadates to a temperature below about 50.degree. C. to effect precipitation thereof, separating the resulting solid ammonium vanadates from the mother liquor and recovering the desired vanadium values.
Other objects and embodiments will be found in the following further detailed description of the present invention.
As hereinbefore set forth the present invention is concerned with a process for obtaining vanadium values from vanadium-containing sources in which the vanadium is present as an oxide in its highest valence state. Heretofore, vanadium-containing materials have been leached with caustic solution in order to solubilize the vanadium, the solubility being dependent upon the concentration of the caustic which is employed. Following this the vanadium was precipitated by acidification with an acid such as sulfuric acid, nitric acid, etc. However, this procedure consumes both the caustic and the acid in the neutralization step and therefore additional caustic and acid were required for subsequent leaching operations. In contradistinction to this procedure, we have now discovered that vanadium values may be recovered by leaching a vanadium bearing material in which the vanadium is present as an oxide in its highest valence state with an ammoniacal medium in which the ammonia is present in a range of from about 1 to about 14 molar, the preferred range being from about 2 to about 8 molar, at elevated temperatures and pressures. The relatively insoluble ammonium ortho- or metavanadate has a much greater solubility at elevated temperatures and pressure, thereby permitting substantial concentrations of vanadium to be recovered. Following the separation of the pregnant leach liquor from the tails the liquid filtrate is allowed to cool to a temperature below about 50.degree. C., thereby precipitating ammonium ortho- or metavanadate which may be thereafter separated from the mother liquor. Alternatively, the pressure which is present may be reduced thereby allowing the soluble ammonium ortho- or metavanadate to precipitate out of solution. The solid vanadium product which is separated from the mother liquor may then be subjected to conventional means of metal recovery such as drying and calcination to form vanadium pentoxide. The vanadium-lean mother liquor may then be passed to an absorber where it is reconstituted with ammonia and water and recycled to form a portion of the ammoniacal media which is utilized to leach the vanadium oxide source.